EPFL's Vincenzo Savona and Romuald Houdr� in the lab [Credit: Alain Herzog / EPFL]

Super-efficient photonic switch created

A super-efficient photonic switch created by scientists in Switzerland could be a major step on the path to optical circuits.

Photonic, or optical, circuits work with light rather than electricity making them 10 to 100 times faster as well as more energy-efficient because they show lower heat loss, better signal-to-noise ratios and are less susceptible to interference.

Emerging photonic circuits use nanoscale ‘optical cavities’ that trap light as switches to control the flow of light, similar to transistors in an electrical circuit, but a major design challenge has been designing cavities that require minimal energy to switch.

Scientists the EPFL laboratory have now fabricated and experimentally tested a silicon-based 'photonic crystal nanocavity' (PCN) that requires an unprecedentedly low amount of energy to operate as a switch.

An optical circuit's total absorbed power depends on the energy required by a single switch operation multiplied by the number of operations per second, so reducing the energy needed to carry out each switch is a major challenge in the design and development of optical circuits.

"In this work we have achieved non-linear effects at a record-low intensity of light," said EPFL scientist Romuald Houdré. "Our structure is also one of the smallest ever designed to show such record nonlinear properties, and it may be built using standard nanofabrication technology.

“This is a very important step along the road to optical circuits, as small size, speed and low power consumption are key requirements for the realisation of an efficient optical switching nano-device."

Non-linear refers to the properties of the optical cavity, which allow it to switch between two different states when subjected to a light signal of sufficient strength. Called "optical bi-stability", this effect is what enables the optical cavity to act as a switch.

Cavities work by confining light in a tiny space of just a few nanometres and the new device, described in an article that features on the cover of journal Applied Physics Letters, features a very high quality, or "Q", factor, which is a measurement of how long the PCN can retain light.

The measured Q factor of the new component, which is made from a silicon slab, is 500,000, meaning that an incoming photon will bounce back and forth inside the optical cavity five hundred thousand times before escaping, which combined with the device’s record small size, produces a higher light intensity for the same energy.

"The nonlinearity is proportional to the intensity and the effect is stronger if you allow for longer build-up times," explained EPFL’ Vincenzo Savona.

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